Field of the Invention
This invention relates to systems and methods for switching between access methods for open data sets.
Background of the Invention
In the z/OS operating system, VSAM (Virtual Storage Access Method) describes an access method as well as various structures for organizing data. VSAM currently includes four data set organizations, namely key-sequenced data sets, relative record data sets, entry-sequenced data sets, and linear data sets. The first three of these data sets contain records that can be of either fixed or variable length. These records may be organized in fixed-size blocks referred to as control intervals (CIs), and then into larger divisions referred to as control areas (CAs).
Currently, requests to access data from a VSAM data set are processed using a base VSAM access method, which uses one of several buffering mechanisms, or a Record Level Sharing (RLS) access method, which operates separately with it's own buffering and caching mechanism. Each access method has its strengths and weaknesses, and only one can be used at any given time to access a data set. To switch between access methods, a user typically must CLOSE the data set and OPEN the data set using another access method. Unfortunately, several different applications or systems may be accessing a data at the same time, which makes closing the data set difficult and/or inefficient. The result is that some applications or systems may be accessing the data set using an access method that is sub-optimal. Although some third-party products have functionality to tune performance within a single access method, these products typically don't have the ability to switch between different access methods when data sets are open.
In view of the foregoing, what are needed are systems and methods to switch between access methods when data sets are open. Ideally, such systems and methods will perform such switching without requiring the data sets to be closed and re-opened. Further needed are systems and methods that always or frequently enable a most efficient/optimal access method to be used when accessing VSAM data sets.